Consider the following homogeneous boundary value problem for function/potential u(x,y) on the infinite strip [−∞,∞]×[0,π/4] w/positive periodic coefficient/conductivity γ(x+1,y)=γ(x,y)>0:
{div(γ∇(u))=0,u(x+1,y)=eμu(x,y),uy(x,y+π/4)=0,γuy(x,0)=−λu(x,0).
The b.v. problem can be moved conformally to an anullus w/a slit.
In the uniform medium γ≡const, Δuk=0 and the solution is of the separable form: uk(x,y)=ceμkx(cos(λky)+sin(λky)),c∈R,
λk=|k| for an integer
k∈Z and, therefore,
λk=|μk|=|k|β(|k|)>0,
where
β≡1.
Let
z=τ(μ)=i(√μ−1/√μ)
and
zk=τ(μk).
The analysis of the reflected/levant finite-difference problem suggests for any positive periodic
γ(x,y)>0:
λk=zkβ(zk)>0,
for an analytic function
β(z)>0 for
z>0, that maps the right complex halfplane
C+={z:ℜ(z)>0} into itself:
β:C+→C+.
In particular
λk's are not negative.
Any intuition for the existence and formula for β(z)? Orientation preserving deformations and winding #s?
The second part of the question is to replace positive coefficient γ(x,y)>0 w/separable α(y)δ(x), such that βαδ=βγ...
This post imported from StackExchange Physics at 2016-01-12 16:10 (UTC), posted by SE-user DVD